12 research outputs found
Finite-Difference and Pseudospectral Time-Domain Methods Applied to Backwards-Wave Metamaterials
Backwards-wave (BW) materials that have simultaneously negative real parts of
their electric permittivity and magnetic permeability can support waves where
phase and power propagation occur in opposite directions. These materials were
predicted to have many unusual electromagnetic properties, among them
amplification of the near-field of a point source, which could lead to the
perfect reconstruction of the source field in an image [J. Pendry, Phys. Rev.
Lett. \textbf{85}, 3966 (2000)]. Often systems containing BW materials are
simulated using the finite-difference time-domain technique. We show that this
technique suffers from a numerical artifact due to its staggered grid that
makes its use in simulations involving BW materials problematic. The
pseudospectral time-domain technique, on the other hand, uses a collocated grid
and is free of this artifact.
It is also shown that when modeling the dispersive BW material, the linear
frequency approximation method introduces error that affects the frequency of
vanishing reflection, while the auxiliary differential equation, the Z
transform, and the bilinear frequency approximation method produce vanishing
reflection at the correct frequency. The case of vanishing reflection is of
particular interest for field reconstruction in imaging applications.Comment: 9 pages, 8 figures, accepted by IEEE Transactions on Antennas and
Propagatio
Bistable diode action in left-handed periodic structures
We study nonlinear transmission of an asymmetric multilayer structure created
by alternating slabs of two materials with positive and negative refractive
index. We demonstrate that such a structure exhibits passive spatially
nonreciprocal transmission of electromagnetic waves, the analogue of the
electronic diode. We study the properties of this left-handed diode and confirm
its highly nonreciprocal and bistable transmittance by employing direct
simulations.Comment: 4 pages, 5 figure
Tunable transmission and bistability in left-handed bandgap structures
We study the defect-induced nonlinear transmission of a periodic structure
created by alternating slabs of two materials with positive and negative
refractive index. We demonstrate bistable switching and tunable nonlinear
transmission in a novel type of bandgap that corresponds to the vanishing
average refractive index, and compare the observed effects for two types of the
bandgaps.Comment: 3 pages, 5 figures; significant change
Sub-wavelength imaging with a left-handed material flat lens
We study numerically, by means of the pseudospectral time-domain method, the
unique features of imaging by a flat lens made of a left-handed metamaterial
that possesses the property of negative refraction. We confirm the earlier
finding that a left-handed flat lens can provide near-perfect imaging of a
point source and a pair of point sources with clear evidence of the
sub-wavelength resolution. We illustrate the limitation of the resolution in
the time-integrated image due to the presence of surface waves.Comment: 4 pages, RevTeX, 6 figures; added references and some discussio
Abnormal phenomena in a one-dimensional periodic structure containing left-handed materials
The explicit dispersion equation for a one-dimensional periodic structure
with alternative layers of left-handed material (LHM) and right-handed material
(RHM) is given and analyzed. Some abnormal phenomena such as spurious modes
with complex frequencies, discrete modes and photon tunnelling modes are
observed in the band structure. The existence of spurious modes with complex
frequencies is a common problem in the calculation of the band structure for
such a photonic crystal. Physical explanation and significance are given for
the discrete modes (with real values of wave number) and photon tunnelling
propagation modes (with imaginary wave numbers in a limited region).Comment: 10 pages, 4 figure
Advice or exercise for chronic whiplash disorders? Design of a randomized controlled trial
BACKGROUND: Whiplash-associated disorder (or "whiplash") is a common condition incurring considerable expense in social and economic terms. A lack of research on effective therapy for patients with chronic whiplash associated disorders prompted the design of the current study. The primary aim of this randomised controlled trial is to determine the effects of a physical activity program for people with chronic (symptoms of > 3 months duration) whiplash. A secondary aim is to determine if pain severity, level of disability and fear of movement/(re)injury predict response to a physical activity program. METHODS / DESIGN: This paper presents the rationale and design of a randomised controlled trial examining the effects of advice and individualized sub-maximal exercise programs in the treatment of whiplash associated disorders. DISCUSSION: This paper highlights the design, methods and operational aspects of a significant clinical trial in the area of whiplash and chronic pain